Not just an Emergency Messaging Service!
While Digital Selective Calling (DSC) is one of the most important parts of GMDSS, it has been the last to be fully implemented. DSC provides a means of automating all day-to-day marine terrestrial calling - making marine radio as easy to use as a telephone. DSC effectively provides the operator with a digital dialing system capable of ringing an alarm at a distant radio station when a call is addressed to that station.
Like a telephone, you do not need to know how the call has been routed or even the frequency or channel being used. All you need is a means of alerting the other party by calling their number, and then a means of talking to them. Under GMDSS, all vessels are allocated a unique Maritime Mobile Service Identity (MMSI), which is a unique nine digit code. The digital calling information is transmitted on specially designated channels. In the case of a VHF radio, this is Channel 70. Channel 70 is dedicated for DSC use and must under no circumstances be used for anything else.
An added benefit of DSC is that the digital dialing signal can also carry other information, such as your vessel’s identity, position and the nature of the call as well as information specifying the channel upon which subsequent communication should take place. The entire message is transmitted in one quick burst, thus reducing the demand time on the calling channel.
In a distress situation, all necessary information can be sent automatically at the touch of a single button. The vessel’s position can be determined from a GPS navigation receiver connected to the radio or entered manually. Its identity is permanently coded into the radio in the form of the allocated vessels MMSI number. The nature of distress can also be selected by the operator if there is time to do so.
Using digital coding, DSC automates all the radio functions with which existing marine operators are familiar. It also relieves the person at the other end from the tedious task of manual watch keeping. All the old familiar functions are still in place, but they now have English names and are accessible at the touch of a button.
The ICS V4 Communication system integrates and makes use of the full range of features and benefits of DSC messaging and Radio Telephony.